1. Field of the Invention
The invention relates to a knob type surge voltage arrester with a gas-filled housing, wherein conically or semi-circularly shaped electrodes are positioned opposite one another and are inserted in the ends of a tubular insulating member. Electrode curvatures facing one another form active surfaces for discharge. On an interior of the insulating member at least one coating of electrically conductive material (an ignition aid) extends over a part of the insulating member.
2. Description of the Prior Art
Surge voltage arresters with two symmetrical electrodes having a truncated conical shape and which are inserted in a gas-tight tube-shaped insulating member are generally known. Due to their shape these surge voltage arresters are called knob or button arresters and are distinguished particularly by small dimensions.
It is furthermore known to provide the electrodes of a discharge spark gap for voltage arresters with approximately a conical or a truncated conical shape (compare the German Pat. No. 1,075,726).
Moreover, surge voltage arresters are known in which at least one coating of electrically conductive material on the tube-shaped insulating member of the surge voltage arrester is provided for lowering the ignition voltage. This coating is in the form of a narrow strip which extends in the direction from one electrode to the other electrode (compare U.S. Pat. No. 3,959,696). Such narrow strips which facilitate the ignition of the gas discharge path by means of field distortion at the electrodes are commonly called ignition strips, ignition lines, or ignition aids. These ignition strips are either connected in an electrically conductive fashion to an electrode or they are mounted on the tubular insulating member such that they are insulated from the electrodes. Such known ignition lines which run in axial directions have the disadvantage that they can lead to secondary ignitions. In the case of secondary ignitions of the ignition strip, the strip assumes part of the discharge which renders the ignition strip ineffective and destroys it.